1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to an apparatus and method for creating an attachment and a seal between two tubulars in a wellbore.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well to a depth whereby the upper portion of the second liner is overlapping the lower portion of the first string of casing. The second liner string is then fixed or hung in the wellbore, usually by some mechanical slip mechanism well known in the art, and cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth.
A recent trend in well completion has been the advent of expandable tubular technology. It has been discovered that both slotted and solid tubulars can be expanded in situ so as to enlarge the inner diameter. This, in turn, enlarges the path through which both fluid and downhole tools may travel. Also, expansion technology enables a smaller tubular to be run into a larger tubular, and then expanded so that a portion of the smaller tubular is in contact with the larger tubular therearound. Tubulars are expanded by the use of a cone-shaped mandrel or by an expansion tool with expandable, fluid actuated members disposed on a body and run into the wellbore on a tubular string. During expansion of a tubular, the tubular walls are expanded past their elastic limit. The use of expandable tubulars as liner hangers and packers allows for the use of larger diameter production tubing, because the conventional slip mechanism and sealing mechanism are eliminated.
If the liner hanger is expanded by a cone-shaped mandrel, then a forgiving material is typically employed between the outer diameter of the liner hanger and the inner diameter of the larger tubular to accommodate any variances in the inner diameter of the larger tubular. It is this forgiving material that provides the mechanism for hanging the weight of the liner below the liner hanger. Typically, the forgiving material is made from a nitrile rubber compound or a similar material.
It is usually desirable to expand the liner hanger to support the weight of a liner and then release the running tool from the liner prior to cementing the liner in place. Typically, the use of the cone-shaped mandrel requires that circulation ports be cut in the wall of the liner, directly below the liner hanger section to provide a fluid path for exiting wellbore fluid and cement during the cementing process. Then, following the cementing process, these ports must be isolated by expanding another elastomer clad section below the ports.
While expanding liner hangers by the cone-shaped mandrel in a wellbore offers obvious advantages, however, there are problems associated with using the technology. For example, by using a forgiving material, such as a nitrile rubber compound, the liner hanging mechanism may only be effectively utilized in a wellbore that has a temperature of less 250° F. If the liner hanger is used in a higher temperature wellbore, then the rubber's ability to carry a load drops off dramatically due to the mechanical properties of the material. More importantly, the circulating ports that are cut into the wall of the liner below the liner hanger diminish the carrying capacity of the hanger due to a reduction of material through this section therefore limiting the length of the liner.
A need therefore exists for a solid expandable hanger that provides for a cement bypass without compromising the carrying capacity of the hanger. There is a further need for a solid expandable hanger that is capable of enduring a high temperature installation. Furthermore, there is a need for an improved expandable liner hanger with a means for circulating fluids therearound.